In recent years, a great deal of attention has been focused on the establishment of optimum climatic conditions in the workplace and home. This attention has produced a variety of air conditioning, filtration and purification devices and processes intended to create germ and dirt free environments in closed, interior spaces.
In workplaces such as an electronic assembly plant, it is well recognized that an out of balance concentration of positive or negative ions should be avoided. In such an assembly plant, workers deal with printed circuit boards having a wide variety of electronic components mounted thereon. These components are susceptible to damage due to static discharge. Because each of the components on the circuit board may not be grounded, it is highly desirable to keep the work area relatively free of static charges. In test facilities where, for example, integrated circuit wafers are tested, it is likewise essential to keep the workplace free of static charges.
It has also been determined that an appropriate concentration ratio between positive and negative ions contributes to the establishment of a healthy, and pleasing environment. Reports on this subject generally conclude that negative ions are beneficial to good health and that a predominance of positive ions, which is typically found to be the case, is detrimental. For the above reasons, ion generators have become increasingly popular.
Several approaches have been taken with respect to ion generation and the achievement of optimum interior climatic conditions. Because negative ions are generally regarded as beneficial, some known ion generators do no more than generate negative ions without any particular regard for the overall concentration ratio between positive and negative ions. Examples of such negative ion generators may be found in U.S. Pat. Nos. 4,244,712; 4,227,894 and 3,910,778.
Other negative ion generating devices are known which attempt to balance the ion concentration ratio by regulating the emission of negative ions. See, for example, U.S. Pat. No. 3,973,927.
Still other ion generating apparatus have been developed which generate both positive and negative ions. In U.S. Pat. No. 2,264,495 for example, a sensor monitors air flow into an ion generator and, in response, the device generates positive or negative ions in order to maintain constant a desired ion concentration. In U.S. Pat. No. 3,936,698, positive and negative ion generators are activated in alternating cycles. In UK Patent Application GB No. 2,117,676, separate negative ion generator and positive ion electrifier devices are used to clean room air.
When ion blowers operate in an out of balance condition and generate a net positive or negative ions, articles adjacent such blowers tend to become charged and may suffer electrostatic damage. In this regard, as noted above, electronic components in an electronic assembly plant are particularly susceptible to damage due to static discharge. In addition, electrically charged particles adjacent an ion generator attach themselves to particulate matter in the air and are attracted to the nearest ground. Thus, adjacent walls and/or equipment often have a dirty film deposited thereon.
Attempts have been made to solve this problem by, for example, adding an electrically conductive particle collector to the outlet of the generator (U.S. Pat. No. 4,250,431), or by mixing negatively charged particles exhausted from a first electrostatic precipitator with positively charged particles exhausted from a second electrostatic precipitator.